1. Field
One embodiment of the present invention relates to a disk drive, and in particular, to a servo writing technique for spiral servo patterns.
2. Description of the Related Art
In general, in disk drives typified by hard disk drives, servo patterns (servo data) used for head positioning control are recorded on a disk medium that is a data recording medium. The disk drive uses the servo patterns read by the head to controllably place the head at a target position (target track) on the disk medium.
The servo patterns recorded on the disk medium have a plurality of servo sectors normally arranged at a fixed circumferential interval so as to constitute concentric servo tracks. The disk drive positions the head on the basis of the servo patterns and uses the head to record user data on the disk medium to construct concentric data tracks.
The servo patterns are recorded on the disk medium by a servo writing Block included in a disk drive manufacturing process. A proposal has been made of a method of recording a plurality of spiral servo patterns constituting base patterns on the disk medium during the servo writing Block (see, for example, U.S. Pat. No. 6,965,489B1).
In the servo writing Block in accordance with the proposed method, a plurality of spiral servo patterns (multi-spiral servo pattern) are recorded, by, for example, a dedicated servo track writer (STW), on the disk medium not incorporated yet into a disk drive to be shipped as a product. The disk medium is subsequently incorporated into the disk drive, which performs a servo self-write method to write radial servo patterns (hereinafter referred to as specified servo patterns for convenience) used for the product to the disk medium. The specified servo patterns constitute the concentric servo tracks.
A method of writing a multi-spiral servo pattern to a disk medium involves using a clock head to generate a clock from a clock pattern pre-recoded on the disk medium. A head seek start timing is generated on the basis of the clock. While performing a radial seek operation on the disk medium, the head writes the multi-spiral servo pattern over the entire surface of the disk medium.
Head seek control is performed by a servo controller in the servo track writer. The servo controller performs the head seek operation in synchronism with a servo clock. If the head seek start timing fails to synchronize with the servo clock, the multi-spiral servo pattern is written to the disk medium at a non-uniform intervals.